Murine AIDS (MAIDS) is caused by a replication defective murine leukemia virus (MuLV) called BM5def. BM5def was molecularly cloned and sequenced to reveal that the virus has a functional LTR and with a single open reading frame in gag gene that encodes a variant Pr60gag. This protein differs from the gag polyprotein of a nonpathogenic ecotropic virus in the carboxyterminus of MA(p15) and throughout much of a p12. The primary purpose of this project is to determine how this single protein contributes to the development of lymphoproliferation and immunodeficiency. Numerous approaches were taken to generate mice expressing BM5def-gag from a transgene. Injection with gag sequences driven by SV40 promote IgH Emu enhancer or MHC Class II Ealpha promoter yields mice bearing the transgenes, but often with no expression of mRNA and in mice having transcripts, no protein. More recently, injections were made with BM5def genomic DNA, again without success. Other laboratories have also failed to generate transgenics using these and other approaches suggesting that the gag gene product may be an embryonic lethal. Vaccinia recombinants bearing the BM5 ecotropic and defective virus gag gene were generated that express the encoded proteins at high levels. Mice immunized and boosted with these vectors were unchanged in their sensitivity to MAIDS. Molecular clones of the BM5 defective and ecotropic viruses were used to generate "bait" for the yeast two-hybrid system to fish out proteins that might bind selectively to BM5def-gag. Two proteins appeared repeatedly in the search and both, when expressed as GST fusion proteins, bind to BM5def-gag expressed from the vaccinia recombinants. The genes encoding these proteins are provisionally designated Defective gag-associated protein 1 (Dgap-1) and Dgap-2.